| In lithium-ion batteries applications, safety problems maybe occurred because ofperformance attenuation of the single cell. Therefore, how to improve these problems usingmonitor circuit has become a growing interest in the application of lithium-ion batteries.But in some special environments, online monitor could not be actualized without wiredconnection. From this point of view, the online monitor system of lithium-ion batteriesbased on wireless transmission was presented in this paper.Effect of the different charge and discharge conditions on the impedance of thelithium-ion batteries was investigated, and the relationship between the impedance andcapacity fad was analyzed. To further analyze the effect of single cell impedance on theperformance of series battery demonstrated that online monitor is important to estimate thebatteries status.AC impedance method was improved and applied in series battery impedancemeasurement system. In this design, phase lock loop used can improve the precision andsimplify the test circuit. Circulating detect method was designed to measure single cell inseries battery. And reference resistance compensation method was used to reduce themeasurement error arising from switch in test circuit. The Impedance online measurementwas put practice in batteries application, and the measurement error of the system was lessthan 2 mΩ.Short distance wireless transmission system, which transmitted the state signal ofbatteries to the monitor terminal, was presented and applied in batteries monitor system.The parameters sampling circuits of lithium-ion batteries were modularized. And theworking mode of monitor system was controlled by the single-chip according to the judgment condition which has been pre-established. This system was optimized throughthe investigation of the power dissipation problem and signal collide problem. Wirelessmonitor of lithium-ion batteries was actualized, and the effective monitor distance was upto 20 meters. |
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